The invention relates to the field of sliding sports and more precisely to that which is known as snowboarding. It relates more particularly to an optimized snowboard-binding highback for the transmission of forces.
As is known, snowboarding may be practiced using different techniques which make use either of stiff boots or soft boots. The invention refers to bindings intended to secure soft boots to the snowboard.
A binding of this type is generally formed by a baseplate, which is screwed onto the board and on which the boot sole rests.
In order to allow transmission of the back thrusts, a binding of this type also includes a highback which is mounted on the baseplate either directly or by means of a rear heel cup passing behind the boot.
In a known manner, the highback is preferably mounted so as to pivot with regard to the heel cup or to the baseplate in order to be folded down forward in order to limit the overall volume of the binding when it is not in use. This highback abuts rearward in its position of use, since the aim of the highback is to provide back thrusts, particularly when the user makes turns on the rear edge, generally known as xe2x80x9cbacksidexe2x80x9d turns.
In point of fact, as the boot used is soft for reasons of comfort, it tends to deform when the user exerts rearward forces and it is necessary for the binding to have a part which receives such forces and transmits them in the direction of the rear edge.
Moreover, it is known that the position of the user""s feet on the snowboard is not exactly perpendicular to the median longitudinal plane of the board, but is, on the contrary, slightly offset.
The front foot is generally oriented more to the front of the board, while the rear foot may be either closer to the perpendicular or slightly oriented forward or slightly oriented rearward.
This latter orientation is more generally adopted by users practicing the xe2x80x9cfreestylexe2x80x9d technique. In this technique, the rider performs a number of figures which require him to move in both the directions of the snowboard, which explains why snowboards intended for this type of riding are symmetrical, i.e. they have two similar tips.
Within the context of this sport, the rider frequently has to perform jumps. Upon landing after a jump, the rider leans forward or backward, and he needs to have a support that can take this force exerted in the direction of movement or in the opposite direction. It will therefore be understood that it is important for the binding to provide support in the direction opposite to that of movement.
To meet this requirement, it has already been proposed to adapt existing bindings, allowing the highback to pivot about the axis of the leg so as to bring it opposite the outer part of the leg, thus corresponding to a support located in the direction opposite to that of movement. This arrangement also has the advantage of releasing the inner part of the leg and facilitates flexing of the latter, particularly when executing figures.
Unfortunately, existing highbacks are insufficiently stiff to provide effective support, particularly given the high degree of momentum exerted when landing after a jump.
Moreover, it is observed that, when the binding is not perpendicular to the median longitudinal plane of the board, it is the outer region of the foot which is closest to the rear edge, and that the support is therefore not provided in an optimum manner.
Solutions have already been proposed which consist in configuring the highback in such a way that it has a portion opposite the outer region of the leg for receiving the forces exerted closest to the edge.
A solution of this type is described, in particular, in document FR 2 769 239.
The solution described in said document consists in giving the highback an asymmetric geometry in which a protruding part is provided on the outer side of the highback, in the upper half of the latter. The objective of a geometry of this type is to allow the take-up of the forces exerted toward the outer rear part of the foot.
A solution of this type nevertheless has many drawbacks.
In point of fact, the protruding region is an element of not insignificant weight, and this weight is added to the rest of the binding.
Furthermore, this protruding region is reasonably fragile since it is located projecting from the actual body of the highback.
More precisely, the region of the join between this protruding part and the rest of the highback is flexible and therefore does not allow the highback to provide all the stiffness that is required, except at the cost of a disproportionate increase in thickness which is reflected in drawbacks in terms of weight and manufacture.
More generally, in order to obtain a sufficiently stiff highback of this type, it is necessary to use a material which is either much thicker or much stiffer, which renders the whole highback heavy and stiff, whereas certain parts of the highback do not require this.
In other words, one of the problems which the invention proposes to solve is the optimization of the geometry and architecture of the highback in order to combine at one and the same time the properties of equired stiffness and optimum transmission of forces while retaining a degree of facility of manufacture and the possibility of varying the stiffness of the highback over its entire surface.
A further drawback of asymmetric highbacks as described in the document cited above, lies in the fact that two molds are required for producing highbacks intended for the right and left feet.
The invention thus relates to a highback for a snowboard binding intended to come into contact with the rear part of the user""s boot in order to withstand back thrusts and having a median longitudinal plane of symmetry.
The highback according to the invention has a stiffer region located asymmetrically with regard to its median longitudinal plane of symmetry.
In other words, the highback according to the invention is symmetrical in its shape but its mechanical properties, particularly its stiffness, are asymmetrical.
The stiffness of the highback is therefore located solely in those places where it is required, which makes it possible for the remainder of the highback to retain a degree of flexibility which may be advantageous in terms of comfort.
It is therefore unnecessary excessively to increase either the thickness or the weight of the highback in order to obtain the required stiffness for effective transmission of back thrusts.
Advantageously, the stiffer region is located on the outer side of the foot, in order to optimize support.
Several embodiments may be adopted. Thus, in a first variant, the stiffer region of the highback may consist of an element embedded inside the constituent material of the highback.
This element may be either a resin-coated glass fabric or a metal grid, or, alternatively, any equivalent element.
In the case in point, a single mold is required for producing not only highbacks intended for mounting on the left binding but also highbacks intended for mounting on the right binding, which reduces manufacturing costs.
In a further variant embodiment, the highback may be produced by multi-injection, one of the multi-injected regions then constituting the stiffer region.
The choice of plastics materials and, in particular, the relative stiffness ratio of the two materials used is optimized in order to obtain the best weight/stiffness compromise.
Advantageously, in practice, the stiffest region may partially traverse the median plane of symmetry of the highback, particularly at the upper edge of said highback, in order to make this variation in stiffness progressive.
The highback according to the invention may be mounted on bindings with or without the possibility of being enabled to pivot about a vertical axis.